Effect of VV-ECMO on CO2 Removal

While the efficiency in delivering O2 has several limitations, removal of CO2 during VV-ECMO is much easier to achieve. While the amount of O₂ delivery is limited by full saturation of arterialized blood and by haemoglobin concentration, a substantial amount of CO2 can be removed from venous blood. In fact, normal venous blood carries around 50 mL of CO₂/100 mL of blood, most of which in the form of bicarbonate ion. When the ECBF flows through the ML, dissolved CO2 is transferred from the blood to the gas side, while new dissolved CO2 is released from carbonic ion assuring a continuous availability of dissolved transferable CO2. In this process, the main limiting factor to the amount of removable CO2 is the partial pressure of CO2 on the gas side, which depends on the ECGF. High ECGF will maintain the partial pressure of CO2 on the gas side close to zero, thus maintaining a high CO2 partial pressure gradient. Indeed, contrary to oxygen delivery, efficient CO2 removal can be obtained with relatively lower ECBF.